The invention relates to the field of methods and installations for changing over the rolls of a rolling mill.
During the operation of a rolling mill, the aging of the work rolls that are in contact with the product to be rolled, or that of other rolls such as the intermediate rolls, or again, although less significant, that of the backup rolls, poses a risk of resulting in the production of a defective rolled product or the damaging of the rolls themselves.
Moreover, during a change-over in type of production, it may be necessary to replace a pair of rolls with another pair of rolls having, for example, a different roughness or a different hardness.
These are the reasons why, from time to time, the rolling mill installation has to be stopped for the replacement of one or more pairs of rolls. In general terms, in the following, reference will be made to the replacement of worn rolls with new rolls, while bearing in mind that the change-over of rolls may be prompted by reasons other than wear alone.
Each of the ends of a roll in a mill stand carries a chock incorporating the bearings allowing the roll to be set in rotation about its axis. In operation, the chocks are capable of sliding vertically in guide slots realized in each of the pillars of the mill stand. In the following, a fitted roll is a roll on which chocks have been mounted.
According to the prior art, a method for changing over rolls comprises a succession of handling operations on the rolls carried out by the maintenance personnel. The sequence of operations is generally as follows:                The extraction of at least one pair of worn rolls fitted with chocks out of a mill stand of the rolling mill. This operation generally demands a device currently referred to as a “dismantling car” fitted with means for the displacement of rolls. According to how modern the installation is, the attachment of the rolls to the body of the roll displacement means is manual or automatic.        The removal of the pair of worn rolls fitted with their chocks to a maintenance zone referred to as the rolls workshop. This operation demands traditional means of handling such as a traveling crane serving the rolling mill plant. Operatives then have the task of trimming slings on the rolls.        A pair of new rolls fitted with chocks is brought from the maintenance zone up to the dismantling car by the traveling crane. The pair of new fitted rolls is put down on the dismantling car. In more modern arrangements, the new fitted rolls can be pre-positioned on the dismantling car by way of suitable devices such as those described in the patent US 2005/000263.        The new fitted rolls are subsequently reinstalled in the mill stand, which can start rolling operations again.        
During this time, the worn rolls fitted with chocks are removed to the rolls workshop. Maintenance operatives withdraw the chocks from the necks of each roll. To this end, the rolls workshop can be provided with a device for extracting and reinstalling chocks of the type described in the document JP-A-63-220913.
The active surface of the rolls is then overhauled by machining on a grinding machine. After an inspection stage on the quality of the re-ground surfaces, the maintenance operatives reinstall the chocks on the necks of the rolls, which are then available to be brought close to the rolling mill.
Such a succession of operations, which is repeated for all the mill stands of the rolling mill, presents certain disadvantages.
Firstly, numerous operations necessitate the intervention of operatives, particularly for the handling of very heavy mechanical elements, in high-risk working zones close to the rolling mill.
Then, the regulations are evolving in order to raise the level of safety in respect of the personnel having to intervene at any phase of operation of the rolling mill.
Additionally, the roll change-over method as a whole is relatively slow. In particular, the inevitable trip to the workshop made by the rolls may deprive the operator of the possibility of quickly switching rolls in case of need, for example in order to adapt the rolling mill to a change-over in type of production. This is particularly true in certain special applications where the quantities rolled in each campaign are relatively small.
Thus, the document U.S. Pat. No. 4,771,626 describes an installation for changing over rolls comprising, from the operative side of the rolling mill, a car fitted with a frame for changing over a group of rolls and means of displacement for the rolls designated as “push-pull” in order to load and unload a group of rolls from the change-over frame. The car is moved close to and away from the mill stand that it serves, in order to extract and reinstall a group of rolls in the corresponding mill stand in the first position, and in order to operate together with a shuttle in the second position. According to this document, the shuttle comprises a single exchange frame similar to that of the car. The shuttle is moved in a direction parallel to the rolling direction, between a position of operating together with the car, the frame of the car and of the shuttle then being aligned for the transfer of the worn fitted rolls from the car to the shuttle or the new fitted rolls from the shuttle to the car, and a position away from the displacement zone of the cars. The installation likewise comprises a rack and a second shuttle. The rack is located away from the displacement zone of the cars, on which the shuttle, likewise fitted with roll displacement means, puts down the worn fitted rolls and loads the new fitted rolls. The second shuttle is used to transfer the worn fitted rolls located on the rack to the rolls workshop and vice versa in the case of new fitted rolls.
According to this prior art, it is necessary to move the empty first shuttle into alignment with the car in order to transfer the worn fitted rolls from the car to the shuttle, to move the shuttle opposite an empty bay of the rack in order to put the worn fitted rolls down there, and then to move the shuttle opposite another bay of the rack in order to load the new fitted rolls. The shuttle is moved into alignment with the car once again in order to load the new fitted rolls there. Finally, the shuttle is moved away from the car in order to be able to move the car toward the mill stand.
But above all, according to the known methods, it is necessary to arrange, at any point in time, sets of rolls fitted with chocks in sufficient quantity to ensure the switching of the rolls. Typically, for a rolling mill with 5 mill stands, 10 work rolls are in service and 10 are on standby in order to ensure the replacement of the rolls in service. This therefore represents the immobilization of (10+10)×2−40 chocks. To this is generally added another set of 10 spare rolls, likewise fitted with chocks, allowing rolls suffering an incident during rolling operations to be changed over quickly, while those dismantled previously are undergoing re-machining by means of grinding in the rolls workshop. The total number of chocks in circulation at any time is thus generally 60. This large number of chocks represents a major investment cost for the installations according to the prior art.